JPH0212800Y2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to a single type electrostatic vibrator.

A conventional general electrostatic vibrator has a vibrating membrane 1' which is held at its peripheral edge by a case 5' and a cover body 12 having a hole 2' for sound wave radiation, as shown in FIG. A fixed electrode 4' having a flat back surface has been provided in elastic contact with a push-up spring 8', but such a conventional example has the problem of large side lobes in the sound wave radiation directional characteristics. In the figure, 11' is a movable electrode, and 3 is a fixed metal fitting.

Therefore, the inventors of the present invention have proposed an electrostatic vibrator in which a vibrating membrane 1, which is a sound wave radiation surface, is concave with respect to the sound wave radiation direction to reduce side lobes, as shown in FIG. That is, the fixed electrode 4 in the figure has a cylindrical shape with a bottom, and the center of the bottom is recessed inward so as to be inclined downward toward the center of the periphery. A large number of holes 2 are formed, and the opening at one end is closed by screwing a case 5. Inside the fixed electrode 4, there are housed membrane fixing devices 9a and 9b that are pressed by a pressing spring 8 attached to the bottom of the case 5, and the peripheral edges are clamped by the membrane fixing devices 9a and 9b. A vibrating membrane 1 is disposed in close contact with the back side of the concave plane portion 4a. The membrane fixing device 9a is made of an insulating material, while the membrane fixing device 9b is made of a conductive material. The peripheral edge of the vibrating membrane 1 is clamped between the inward facing collar of the membrane fixture 9a, and a back plate 10 serving as a sound wave shield is formed at the bottom of the membrane fixture 9b. The vibrating membrane 1 has a movable electrode 1 on the surface on the back plate 10 side.
One polarity of a vibration power source (not shown) is connected to this movable electrode 11 through a membrane fixture 9b and a pressing spring 8.

When, for example, a driving power source is connected between the movable electrode 11 and the fixed electrode 4 and the vibrating membrane 1 is vibrated, sound waves are radiated upward in the figure through the holes 2.

By the way, as shown in FIG. 3, the electrostatic vibrator has a relationship between the output sound pressure and the wavelength of the sound wave at the driving frequency as shown by the broken line. If the distance (hereinafter referred to as the back chamber dimension) to 10 is n/2λ (n = 1.2...positive integer) such as λ/2, λ, 3λ/2, 2λ, the output will be as shown by the solid line in the same figure. There is a risk that the sound pressure level will drop and the beam pattern will change.

The present invention was devised in view of this point, and its purpose is to provide an electrostatic vibrator that can efficiently output sound waves.

However, in the case of the embodiment, the back chamber dimension l in FIG.
is set to be less than 1/2 of the wavelength at the maximum usable frequency so that the equation l=n/2λ does not hold.

In this invention, a large number of holes are made to allow sound waves to pass through, and a vibrating membrane is installed on the back side of a fixed electrode with a concave surface on the front side and a convex surface on the back side. The sound wave radiation direction of a certain vibrating membrane is concave, and the distance between the vibrating membrane and the sound wave blocking back plate provided on the side opposite to the sound wave radiation direction of the vibrating membrane is less than 1/2 of the sound wave wavelength at the frequency used. This has the advantage that the level of the output sound pressure does not become small, so that changes in the sound wave pattern can be prevented, and sound wave radiation can be performed reliably and efficiently.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of a conventional example, FIG. 2 is a sectional view of an embodiment of the present invention, and FIG. 3 is a diagram explaining the principle of the same. 1 is a vibrating membrane, 2 is a hole, 4 is a fixed electrode, is the back plate, and l is the back chamber dimension.

Claims (1)

[Scope of utility model registration request] A vibrating membrane is installed on the back side of a fixed electrode with a concave surface and a convex surface on the back side, which has many holes for the passage of sound waves, and has a concave surface on the front side and a convex surface on the back side.The vibrating membrane is a sound wave emission surface facing the fixed electrode side. The sound wave radiation direction is a concave surface, and the distance between the sound wave blocking back plate provided on the opposite side of the vibration membrane to the sound wave radiation direction and the vibration membrane is less than 1/2 of the sound wave wavelength at the operating frequency. Electrostatic type vibrator.